In casting of ferrous and non-ferrous products, metal is melted in a melting furnace. The metal is transferred from the melting furnace into a dosing furnace. The molten metal is stored in a molten state in the dosing furnace ready for delivery to the mold. A metered amount of molten metal is delivered to the mold. To produce a high quality cast metal product, a clean molten metal must be delivered to the casting chamber. Furthermore, the inlet of the dosing tube is very small so to increase the service life of the dosing tube, a clean molten metal must enter the dosing tube en route to the casting chamber.
A clean molten metal must be delivered to the mold also to produce a high quality cast metal product. Integrity, properties, and surface appearance are important qualities of aluminum cast foundry alloy components as well as other metals used in automotive, electronic, appliance, and other exacting applications. Filtering impurities, such as oxide inclusions and intermetallic sludge, eliminates hard spots that the impurities may cause in machining. Some prior art attempts have been made to filter the molten metal prior to entry into the dosing tube. U.S. Pat. No. 5,370,171 discloses an exit filter that the metal flows through prior to entering a suction tube. The patent discloses a subcompartment into which a suction tube is placed. The subcompartment has solid walls and a filter at its bottom where the metal is required to flow through prior to entering the subcompartment and then the suction tube. The patent discloses that the filter could be placed on a bottom of the suction tube, but, according to the patent, the subcompartment is preferred because it permits the use of a larger expanse of the filter. Hence, a need arose to provide a large surface area filter that can attach directly to the bottom of a dosing tube.
Furthermore, the inlet orifice of the dosing tube is exceptionally small. Any filtering device cannot plug this orifice and it must permit substantial metal flow when the furnace unit is pressurized to deliver a precise quantity of molten metal through the dosing tube into the casting apparatus. The filter configuration herein described satisfies and overcomes this restraint.